Project Summary/Abstract Group B streptococcus (GBS) is the most prevalent cause of perinatal infection, with mortality and profound comorbidities for neonates. Vaginal and gastrointestinal (GI) colonization with GBS occurs in up to 30% of adult women, with highest rates in African Americans. Pregnant women can pass GBS to their fetuses during vaginal birth, putting them at risk for Early Onset Group B Streptococcus Disease (EOGBSD), which is associated with a neonatal mortality rate of 5-10% and morbidity of approximately 50%. The Centers for Disease Control and Prevention (CDC) 2010 guidelines require universal antepartum GBS screening by vaginal to rectal cultures of all women at 35-37 weeks gestation, and intravenously administered intrapartum antibiotic prophylaxis (IAP) of two or more doses if a woman is found to be colonized with GBS. While use of these guidelines has significantly reduced EOGBSD incidence from 1.7 per 1,000 live births to 0.34-0.37, up to 30% of laboring women and their fetuses are exposed to IAP. Complications associated with IAP are significant for both the mother (increased incidence of antibiotic resistance, allergic sensitization, diarrhea including Clostridium difficile, and fungal infections) and neonate (gut dysbiosis, opportunistic infections, and allergic risk). The proposed study will test a low-cost, safe, innovative approach to reduce prenatal colonization with GBS, while adhering to CDC guidelines for EOGBSD prevention. We hypothesize that women who ingest a commercially available oral probiotic combination product (Florajen3, containing Lactobacillus acidophilus, Bifidobacterium lactis, and Bifidobacterium longum) daily from 28 weeks gestation through the time of labor will have a lower risk of GBS colonization compared to women taking placebo. The purpose of this Phase 2 placebo-controlled, double blind, randomized controlled trial (RCT) is to determine the efficacy of once daily ingestion of Florajen3 by healthy low-risk pregnant women from 28 weeks gestation until the time of labor to (a) reduce the proportion of women with GBS colonization and thus (b) reduce the number of women who receive IAP. We expect this intervention to alter the vaginal and rectal microbiota by (c) increasing Lactobacillus colony counts, (d) decreasing GBS colony counts, and (e) reducing GI symptoms. In preparation for this RCT, the research team has conducted two preliminary studies (one in vitro, one in vivo), an integrative review of the literature regarding the use of prenatal probiotics, and a systematic review on probiotics and urogynecologic infections. The literature and preliminary work support the safety, tolerability, and potentially high impact of the oral probiotic as an innovative, low-risk, easy-to-use intervention to reduce GBS colonization during pregnancy and significantly reduce exposure of mothers and infants to IAP and the associated complications. If positive, findings from this study will shift the paradigm in clinical practice and be used to design and conduct a larger RCT to extend the science of nursing, midwifery, obstetrics, microbiology, clinical nutrition, and infectious disease for care of pregnant women and their infants.